The objectives of this proposal are to investigate the mechanisms and development of bile acid in the developing intestine of the neonate. Intestinal perfusion studies and isolated segments of proximal jejunum and distal ileum are being performed to characterize rates of bile acid transport at different postnatal ages. To further define these mechanisms, microvillus membranes have been isolated from the ileum and jejunum and bile acid transport has been characterized in isolated membrane vesicles. The lipid composition and physical characteristic of membrane vesicles will be defined so as to better define the maturational factors which influence bile acid transport, and thus limit nutrient absorption in the neonate.